The rising popularity of indoor tanning, an artificial source of ultraviolet radiation (UV) raises concerns that the melanoma epidemic will continue to cause unnecessary morbidity and mortality. Most epidemiologic studies of this risk factor and melanoma predate the introduction of modern tanning equipment (ca 1980), thus new epidemiologic studies are urgently needed among individuals with substantial levels of exposure and collection of detailed exposure information. In addition, our understanding of the role of DNA repair in modifying the risks of melanoma associated with UV exposure is just emerging. The specific aims of our proposal are to assess whether frequent and/or long-term use of modern era indoor tanning increases the risk of melanoma, and whether the risk of melanoma may be influenced by variation in inherited polymorphisms that affect DNA repair. We propose to conduct a population-based case-control study of melanoma among 2660 residents of Minnesota (1330 cases, 1330 controls), ages 25-59, a group found to have a high prevalence of exposure to indoor tanning. We will identify cases through the Minnesota Cancer Surveillance System, a pathology-based, statewide cancer registry of high quality and completeness for case ascertainment. Each case and control subject's history of exposure to indoor tanning, and to potential confounders will be collected during a telephone interview. Buccal cell samples from cases and controls will be collected for DNA. Associations between indoor tanning or impaired capacity to repair DNA and melanoma will be measured by the odds ratio, controlling for known confounders. Differences in risk of melanoma associated with exposure to solar or artificial ultraviolet radiation will be explored by skin type and by DNA repair pathways specific to the repair of UVB- or UVA-induced DNA damage in skin. Except for sun exposure, established risk factors for melanoma, such as skin type or family history, are not amenable to change. Indoor tanning behavior, however, is under the control of the individual. If well-designed epidemiologic studies confirm that indoor tanning is a risk factor for melanoma and that some individuals are particularly susceptible to its effects, public health action may be indicated to discourage use and reduce the risk of the melanoma.